This invention relates to a method and apparatus for slicing a cylindrical elastic body, for example a broad belt, in order to divide it into narrower width belts and/or rings, the broad belt being hereinafter referred to as a slab.
A method for slicing a slab into rings by means of a two-shaft system is generally used in the prior art because a change in the internal size (bore) of the slab does not require a change of a shaft, and accordingly the time for resetting is short.
The following prior art method has been proposed for slicing a slab into belts of a certain width by means of the two-shaft system. According to this method, as shown in FIG. 7(a) and (b), a slab A is placed across a horizontal drive shaft 10 and a horizontal tension shaft 30' arranged in parallel and at a distance with each other. Then the top end (on the right-hand side of the drawing) of the tension shaft 30' is tilted in its horizontal plane to move the top end of the shaft 30' away from the drive shaft 10 and expand or stretch one end portion of the slab A. With the slab A being tensioned such as to tend to move towards the root ends (the left-hand side of the drawing) of both the shafts 10 and 30', the drive shaft 10 is turned to rotate the slab A in one direction so as to bias the slab A, due to the tension, towards the root ends of both the shafts 10 and 30'.
Thus, with the slab A being rotated and biased towards the root ends of both of the shafts 10 and 30', a cutter (not illustrated) is moved to cut into the slab A adjacent the drive shaft 10 to slice it into rings or belts of desired widths. The cutter is made to travel stepwise from the top (right) end side of the slab A towards the root end side thereof by a distance corresponding to the desired belt width to effect cutting. A slab A itself has an inherent tendency to bias or move due to the manner of laying of the cores, canvas and cords or some other causes. If such a biasing tendency is strong and the slab A does not move towards the root end, the direction of rotation of the drive shaft 10 is preferably changed. FIG. 8 is a flow chart showing the foregoing procedure of the conventional slicing method described above.
The aforementioned conventional method presents the following problems:
(1) The slab A is biased towards one end by expanding the slab A on one end side by means of the tension shaft 30', thus generating a tension in the slab A. If the tension is small, the effect of biasing the slab A will be small and cannot reliably bias the slab A towards the root ends of the drive shaft 10 and the tension shaft 30'.
Furthermore, even if a sufficient tension is generated to bias the slab A towards the root ends of both of the shafts 10 and 30', the tension in the slab A will be gradually reduced when the slab A is sliced stepwise at a constant interval from its top end side (which has a larger tension) to the root end side and the cutter approaches closer to the root end side. Thus the effect of biasing the slab A towards the root end side of both the shafts 10 and 30' will decrease, which in turn may cause a discrepancy between the starting point and finishing point of a slice; consequently a defective belt with stepped cutting (the termination of a cut is not aligned with the beginning of a cut) may be produced or the belt width may change.
When the slab A is biased under the influence of the tension caused by the tension shaft 30', although the slab A itself has a biasing tendency in the opposite direction (towards the top ends of said both shafts), the tension acting on the slab A will be reduced gradually as the slab A is sliced into rings at a constant interval by a cutter from the top end side of the slab A. Thus the balance of power might be lost suddenly and the slab A might shift towards the top end resulting in defective cutting.
(2) As described above, the top end side of the tension shaft 30' is tilted with respect to the drive shaft 10 in the horizontal plane to separate the tension shaft 30' away from the drive shaft 10, and in turn, apply a tension to the slab A. The greater the tilt angle of the tension shaft 30' with respect to the drive shaft 10, the greater will be the distance between the top end of the drive shaft 10 and the top end of the tension shaft 30'. When the difference (maximum inter-shaft distance .delta.) between inter-shaft distances at both ends of the slab A exceeds a certain value, stepped (defective) slicing will happen. To be more specific, as shown by two graphs on the right side of FIG. 9, for slabs having a circumference of 132 mm or 63 mm, stepped slicing will occur when the maximum inter-shaft distance exceeds 1.0 mm. It, therefore, is necessary to set the maximum inter-shaft distance .delta. within 1 mm. This, however, tends to cause the problem described in (1) above since the biasing effect is small. As shown in FIG. 9, the biasing distance corresponding to rotation for a fixed time (15 seconds) is as very small as about 6 mm. FIGS. 11(a) and (b) are graphs showing the relationship between the tilt angle .theta. of the tension shaft 30' and the biasing distance (towards the root end) after rotation for a fixed time (15 seconds) for five kinds of slabs of which the circumference ranges from 68 to 132 mm.
(3) From the viewpoint of belt quality, it is not desirable to produce a large tension in the slab.